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Amorphous Core Output Transformers

Lundahl Amorphous Core Output Transformers
(A Review)

This review concerns the effects observed upon switching the standard Lundahl (silicon-iron core) output transformers in my power amplifiers, to Lundahl’s new (amorphous core) output transformers.

My current stereo system (for context):
1. Analog: Basis Audio 2001 turntable, Basis Audio Vector tone arm, Audio-technica ML-150 MM cartridge
2. Digital: Arcam DVD/CD player, Adcom 575 CD player

1. Phono-stage: McIntosh MX 113, and Lehman Audio Black Cube
2. Bent Audio TX102 MK.II tapped transformer passive preamp

1. K&K Audio 300B push/pull (20 Watt, 3 stage, class “A”, all transformer coupled, zero feedback, mono-blocks)

1. Reimer McCullough GS monitors (94db, 4ohm; M-T-M design)
1. Synergistic Research

It seems useful to note some things at the very beginning. Previous reviews are few in number, far too understated and too brief. This proves to be less than helpful in convincing the would-be buyer that the significant increase in cost is worthwhile (especially in a product that cannot be easily returned once tested). Furthermore, these new transformers require “burn-in” time and this has only added to the buyer’s hesitation. The purpose of this review therefore, is to hopefully help shed some much needed light on this rather SIGNIFICANT new transformer technology, and dispel some of the fear attached to the pursuit of the unknown.

The question of “burn-in”
Yes they need burn in. No, I don’t know why. Quite frankly, I don’t really care either. Some people will tell you that “burn-in” is psychological as your brain adjusts to the new sound. Well, this did not pertain to my situation; I never got to hear the initial “burn-in” period. That was taken care of for me by Kevin Carter of K&K Audio, who happened to install my new amorphous core transformers. For me, I simply had them dropped off at K&K Audio, and five days later, picked them up. What I did hear, was something profoundly different than what I had heard five days previously in my old system.

Kevin informs me that the most critical and sonically relevant “burn-in” period is about the first 50 hours. Once started from cold, at hour zero, they apparently sound rather similar to their silicon-iron counterparts. However, the similarities begin to diverge rather noticeably at about hour 10, at which point the transformers begin to sound like completely different entities all together, and by hour 50 you have in short “arrived”. Kevin did make it clear to me that the amorphous core transformers would continue to improve over time, but that the changes would grow less dramatic at this point (after hour 50) and be spaced farther and farther apart. In other words, they would continue to improve but the new improvements would be more like refinements and happen slowly even for months.

I cannot describe for you the first 50 hours of “burn-in” (except to describe the initial sound difference from the old transformers later in this review), but I can tell you what has happened regarding their continued “burn-in” since the several hundred hours I have put on them over the last few months. I would say that once I had received the mono-blocks back from K&K Audio, the sound improvement was jaw-dropping (more on this later). I then set out to give the new transformers a rather serious musical workout for several hundred hours to see if they would indeed improve any further. What my wife and I experienced was that the amps sounded noticeably better after an additional 50 hours was worked through them (so about 100 hours from hour zero). Following this, the amps became more refined, open, and subtly nuanced at about the 200 hour mark. Lastly, they have as Kevin said, continued to improve, essentially growing more musical with each passing month. My wife and I never had the feeling that we were missing out on something as the transformers were going through this “burn-in” process. Quite the contrary, we were thrilled with the substantial improvement over what we had heard from our amps before; the continued improvements over time simply seemed like icing on an awesome cake.

“The Switch” (our amps with the new amorphous core transformers arrive)

How do they sound compared to the standard silicon-iron transformers? Let me make two things abundantly clear:



I am not kidding, I was not prepared for what I kept hearing and what I kept getting more and more of (though less and less over time). I am reluctant to say this as readers may get the wrong idea, thinking that the older version of Lundahl transformers were in some way flawed, but that is not the case. Traditional Lundahl transformers are excellent, one of the very best out there (some consider them to be the very best). However, Lundahl’s new amorphous core output transformers simply make the old ones sound broken. There, I’ve said it; and no, I am not exaggerating. The improvement in fidelity in our system is so significant that I keep asking myself if my amps had been broken before. Did Kevin tweak my amps or fix something that he had failed to tell me about? “No David, I simply swapped out the old transformers with the new amorphous core output transformers and burned them in for about 50 hours to make sure everything was behaving properly. Nothing else was done to your amplifiers. They were not altered in any other way.”

The Sound
Listeners I am sure will respond to the new sound’s overall gestalt differently, in accordance with their various tastes, stereo system’s idiosyncrasies, etc. However, I believe the following characteristics will stand out to most:

a) Music happens outside the speakers. At times the speakers don’t even seem to be on (how a transformer core material is responsible for this beguiles me)
b) Far more dynamic; and a sense of greater power.
c) Frequency extremes have increased or can now be heard for the first time.
d) Natural, instruments sound like themselves rather than synthetic copies.
e) Lower noise floor. There is a quieter and blacker background. There is less hash, less grunge, less pain.
f) Transparent; it is as if the transformer was removed. The window was replaced with open air.
g) Effortless, everything seems less stressed
h) Greater detail and resolution

I once wrote to Marc Mickelson (editor of Soundstage! online magazine) asking him exactly what it was about the very best equipment that moved him so. He stated simply “they breathe”. He explained in our correspondence that with the best equipment music flowed rather than being manufactured artificially. I must borrow his expression here since I feel it best describes the overall experience of listening to music through the new amorphous core output transformers, “they breathe” with the music.

Kevin at K&K Audio tells me that the amps’ bandwidth measure the same, as well as the power. He admits that the sonic differences are from a measurement perspective “mysterious”, but empirically, readily hearable. I like Kevin’s attitude. He doesn’t use “BS” to sell his products and he isn’t afraid to admit when he doesn’t know something. As he says “I could tell you the theoretical reason for an amorphous core’s sonic advantage over that of its silicon-iron counterpart, but it still fails to explain the wholesale improvement we hear in the real world.” Regardless of how they measure, what my wife and I hear is that, in short, EVERYTHING is better. This is why I quote Mickelson on the “breathe” characteristic, it is the only hypothesis I can suggest for the improvement. Rather than increasing the frequency response (my amps were already excellent in this regard), increasing the power, or whatever, I believe the new transformers are doing something akin to letting the music through more faithfully and more easily. In a word it is an increase in overall “fidelity”. The amps sound faster, able to “get out of the way”. The transients just happen, the notes decay naturally, and the harmonic envelope that surrounds each instrument glows more life like. You are encouraged to follow the music from its softest whisper to its loudest crescendo without fear of pain or fatigue the way we use to, unconsciously tensing up before the momentary bite would occur. I am not saying that this cannot get better; it already got much better than I thought was possible. Yet, there is now simply less of this “strenuous” experience. Music is fun again. I hadn’t realized how much of the sweetness of music could be had in a playback system.

I love music. I have always delighted in hearing live orchestras and symphonies. Classical music, one of the last audible art forms that is regularly un-amplified is glorious to experience live. Sadly, however, I have not found this to be true when reproducing the same at home. Traditionally when played through most stereo systems, I have come away feeling as though I had just eaten instant mashed potatoes instead of the real thing. In contrast, rock and pop have not been so unpalatable and I think this may be the result of their extensive use of amplified, distorted and synthesized sounds. My ears seem to buy the illusion. However, the cello in a music hall un-amplified either sounds like it does live, or it sounds like elevator music. The point here is that with the new transformers, I am now listening to classical music 80% of the time! This is not to say that rock and pop now sound bad, on the contrary, its just that now a violin sounds like a violin, and “wow” is that a joy to hear.

With 20 watts or so, one is encouraged rather persuasively to seek speakers of higher sensitivity. I have often considered increasing the power of my amps due to this very issue. Too many of the very good speakers out there do not come in the 96db and higher flavors. However, as I mentioned earlier, one of the results of the transformer switch was a perceived sense of greater power in the amps. Again, Kevin made it clear that the output power remained the same in the measurements. I can only surmise that this is due to that quality of the new transformers to “get out of the way” of the music. It is the same quality that has made them more dynamic, possessing a lower noise floor, more transparent, faster, etc. We have found that we can turn the volume up much higher than before without a sense of distortion, strain, or pain. The significance is that I am no longer concerned about the output power of my amps. I am not looking for more power; I am looking for more of what these amorphous cores give me, which is MORE MUSIC. If I had doubled my output power instead of switching to the amorphous core transformers, I would only have doubled the volume of what I had before, and remember I now feel as though the old version of my amps sounded broken. Why would I want a 40 watt broken amp? Do I really need twice the pain in my music?

Bottom Line
The new Lundahl amorphous core output transformers have wrought one of the greatest if not the greatest improvement in my stereo system, and my wife confirms this. I can’t speak to the SE version as my amps are PP, but if it is anything like this you are in for a shock. It does not turn your home system into live music, but it does help to create a far more convincing illusion of it; one that is very satisfying to listen to. I would equate the change we have heard in our home as equal to buying new speakers. What amazes me is that this was produced by only changing the core material of an output transformer.

David Vair

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Topic - Amorphous Core Output Transformers - davidvair 07:23:42 01/19/05 (9)

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